1. Field of the Invention
The present invention relates to a method and system for reproducing multi-channel surround audio signal such as 5.1 channel surround audio signal.
2. Description of the Related Art
Audio-visual reproducing systems called home theaters are being widely used. The audio-visual reproducing system reproduces video from a digital versatile disk (DVD) on a relatively large-screen display while using a multi-channel surround audio system such as 5.1 channel surround audio system for sound reproduction. The audio-visual reproducing system thus reproduces powerful audio-visual content.
The 5.1 channel audio-visual reproducing system uses four types of speakers, a speaker in front of a listener (hereinafter referred to as front speaker), a speaker in center front of a listener (hereinafter referred to as a center speaker), a speaker in rear of the listener (hereinafter referred to as rear speaker), and a speaker dedicated to low-frequency sound. A subwoofer as a low-frequency speaker is responsible for monophonic sound in a band of 100 Hz or lower. The other speakers work in a range from 100 Hz to 20 kHz.
A typical known 5.1 channel audio-visual reproducing system is shown in FIG. 31. As shown in FIG. 31, a front left channel speaker 10FL is placed in front left of a listener 4, a front right channel speaker 10FR is placed in front right of the listener 4, and a center channel speaker 10C is placed in center front of the listener 4.
Furthermore, a rear left channel speaker 10RL is placed in rear left of the listener 4, and a rear right channel speaker 10RR is placed in rear right of the listener 4. A subwoofer 10SW as a low-frequency effect (LFE) channel speaker is arranged at any convenient location.
The six speakers 10FL, 10FR, 10C, 10RL, 10RR, and 10SW are housed in the boxes thereof, and placed at the locations thereof. The six speakers are typically spaced from the listener 4 by a distance ds of about 2 meters.
In the known audio-visual reproducing system, a speaker box having a volume of 15 liters was used for the front left and right channel speakers. Currently, each of the front left and right channel speakers, housed in a small box having a volume of about 1 liter, is also referred to a satellite speaker. Since these speakers are naturally unable to provide low-frequency sound, and to compensate for this, a speaker dedicated to low-frequency sound, called a subwoofer, is added. If the speakers other than the subwoofer are housed in the small boxes, a cross-over frequency of the audio signal supplied to the subwoofer 10SW is typically 150 Hz, slightly higher than typical 100 Hz, but still a sufficiently low frequency.
In the speaker system thus configured, a sufficient low-frequency sound is generated when a 5.1 channel audio signal is reproduced from a DVD. Furthermore, since a reproducing side also includes a special channel particular for a low-frequency sound, the low-frequency sound is fully provided within the room in a manner that has never been performed before. The user thus can enjoy the powerful presence of sound and video.
However, a small room made of weak wall and floor material may not have a sufficient space to accommodate the six speakers, and may result in a noise problem due to sound leakage to the outside of the room.
When a user wishes to enjoy a powerful audio sound in audio-visual content from a DVD with an ordinary 5.1 channel speaker system, a sound level of 90 dB or higher is required. Noise problem to the ambient environment needs to be addressed when the user attempts to enjoy the effect of the multi-channel sound.
Even a single door or wall can easily isolate sound if the sound is high frequency. However, a low-frequency sound as low as 100 Hz or so cannot be easily isolated. A small room is not sufficient to isolate the low-frequency sound. In particular, a sound of 40 Hz to 50 Hz, handled by the subwoofer, resounds well, and propagates throughout a relatively wide area.
The sound reproduced by the subwoofer may leak out not only to a next room but also to rooms upstairs or downstairs, thereby possibly annoying persons in the next room. The lower the frequency of the sound, the more difficult the isolation of the sound is. The subwoofer is a problem and the otherwise excellent 5.1 audio reproducing system cannot be fully enjoyed.
Japanese Unexamined Patent Application Publication No. 5-95591 discloses an audio reproducing system in which an intermediate to high frequency sound is reproduced by a small speaker (housed in a speaker box) and a low-frequency sound is reproduced in the vicinity of the ears of the listener with a low-frequency headphone or using a bone conduction mechanism.
In accordance with the disclosure, the low-frequency sound is reproduced using the headphone or the bone conduction mechanism. The low-frequency sound, heard at a high level by the listener, does not propagate to next rooms or a next house.